BRASILIA —
President Dilma Rousseff's approval rating plummeted and her re-election chances have dimmed in the month since massive protests of poor public services, corruption and other complaints shook Brazil, a new poll published on Tuesday showed.

The number of Brazilians who approve of her government's performance fell to 31.3 percent in July from 54.2 percent in June. The number of those who think it has done a bad job soared to 29.5 percent from nine percent, the survey by polling firm MDA Pesquisa said.

The poll is the second to be released since the protests began. A previous survey, by pollster Datafolha, also suggested that the myriad factors that led to the demonstrations, from the high cost of living to the poor quality of public health and education, have quickly undermined Rousseff's once-towering approval ratings.

According to the new poll, commissioned by private transport sector lobby CNT, Rousseff's personal approval rating fell to 49.3 percent in July from 73.7 percent in June. Negative evaluations have risen to 47.3 percent from 20.4 percent a month earlier, and are now almost at break-even with the positive.

Together, the slipping poll numbers raise new questions ahead of what previously seemed an easy re-election for Rousseff, who is expected to run again in presidential elections next year.

Voting intentions for Rousseff dropped to 33.4 percent from 54.2 percent before the protests. The fall suggests she would no longer win a first round election outright and would likely have to face a rival in a run-off.

Almost 45 percent of those polled said they would not vote for Rousseff under any circumstances, which would complicate her prospects in a second-round vote.

Former environment minister Marina Silva and Minas Gerais Senator Aecio Neves appeared to be her strongest adversaries, with 20.7 and 15.2 percent of the voting intentions respectively. Silva's show of support was especially strong, bouncing up from just 12.5 percent of those surveyed in the last poll.

The daughter of illiterate Amazon rubber tappers and a former Green party presidential candidate, Silva's candidacy is uncertain because she is currently founding a new political party that might not be ready to run by election deadlines.

Her popularity, though, stems from the fact that she isn't identified with the existing political establishment. “Marina is the politician that has capitalized most from the protests,” said Clesio Andrade, head of the CNT.

Until recently, Rousseff had enjoyed some of the highest approval ratings of any leader in the Western world, largely thanks to record-low unemployment. Her popularity started to slip in early June as rising consumer prices began to eat away at Brazilians' purchasing power, a sure recipe for trouble in a country with a long history of runaway inflation.

Then came the nationwide street demonstrations that sent shockwaves through Brazil's political establishment. While the protests have not been directed at a single leader or party, widespread discontent with a ruling class that is seen as self-serving and corrupt has eroded the popularity of politicians at all levels, including Rousseff.

A striking worker carries a large effigy of Brazil's President Dilma Rousseff during a protest in Sao Paulo, Brazil, July 11, 2013.

The CNT/MDA poll showed that 84.3 percent of Brazilians approve of the protests that drew one million people onto the streets of Brazil's main cities when the they peaked in June. The poll said the main factor fueling the sudden outburst of anger was discontent with corruption in Brazil, followed by bad health services and overspending on soccer stadiums for next year's World Cup in Brazil.

Rousseff's main response to the protests was to promise political reform. Her plans to consult Brazilians through a constituent assembly or plebiscite, though, met stiff opposition in Congress, even among her ruling Workers Party.

Despite the setbacks, Rousseff remains the leader among potential candidates. “She is still a very competitive candidate and the leader of the pack,” said Brazil analyst Joao Augusto Castro Neves at the Eurasia consultancy in Washington.

Still, her decline in the polls has led some members in her party to openly advocate the return of her mentor, former president Luiz Inacio Lula da Silva, still Brazil's most popular politician.

If Brazil's sluggish economy deteriorates into recession and unemployment rises, the chances of Lula running again for president increase - even if age and health remain a concern for the 67-year-old cancer survivor, Castro Neves said.

The CNT/MDA poll of 2,003 people was conducted July 7-10. The study has a margin of error of 2.2 percentage points.